Video game processing method, video game processing apparatus and computer readable recording medium storing video game program

ABSTRACT

A simple model for an object to be processed is obtained, and Z-values and display coordinates of vertexes of the simple model from a predetermined viewpoint are calculated. A rectangular Z-area associated with the calculated display coordinates is detected, and an area of a predetermined size is generated based upon the detected Z-area while keeping a feature of the detected Z-area. A minimum value Z1MIN of the simple model is extracted. The minimum value Z1MIN of the simple model is compared with all of the Z-values within the generated area, which are stored in a Z-buffer at that time. If it is determined that the minimum value Z1MIN of the simple model is larger than the maximum value Z2MAX within the generated area, subsequent steps are skipped. Thus, processing of a real model can be avoided, which reduces the processing.

CROSS REFERENCE TO RELATED APPLICATION

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2001-364858, filed on Nov. 29, 2001, thedisclosure of which is expressly incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to video game processing. Moreparticularly, the present invention relates to displaying a virtualspace from a virtual viewpoint on a screen.

2. Description of the Related Art

A role playing game (called “RPG” hereinafter) is known as one videogame genre. In a RPG, a character plays a role in a game instead of aplayer. In general, the player experiences a pseudo adventure through acharacter manipulated by the player (called “player character”hereinafter) so as to develop a story. In many cases, a player characterand characters fighting against the player character (called “enemycharacter” hereinafter) are set in zones formed in a virtual space. Theplayer character advances to each zone, where the player characterfights against the enemy characters that prevent the player characterfrom achieving his/her goal in the story. In addition, the playercharacter obtains items that provide advantages during the fights anddefeats the enemy character so as to develop the story.

In order to display an image from a certain viewpoint in a video gamemachine for implementing an RPG by displaying objects such as a playercharacter and an enemy character in a virtual space on a screen, anobject to be hidden behind a predetermined object is not displayed. Forexample, Z-buffer processing is used for removing hidden-parts. As atechnology relating to the Z-buffering, an image synthesizing apparatusand an image synthesizing method are disclosed in Japanese UnexaminedPatent Publication No. 8-161526, for example.

However, multiple characters may be required to be displayed on a singlescreen in a conventional RPG. As a result, a processing amount involvedin the Z-buffering is increased. Thus, there is a problem that thenumber of displayed characters may be limited due to the processingcapacity of the game machine. Similarly, when a character is required tobe displayed in more detail, the number of polygons forming thecharacter tends to increase. As a result, a processing amount involvedin the Z-buffering increases as the number of polygons increases. Then,there is a problem that a number of polygons that can be used for othercharacters may be limited.

SUMMARY OF THE INVENTION

The present invention is made in view of these problems. It is an objectof the present invention to provide a video game processing method, avideo game processing apparatus and a computer readable recording mediumstoring a video game program, which allow a more detailed character ormore characters to be displayed in a video game by achieving fastrendering processing.

In order to overcome the problems and to achieve these objects,according to first aspect of the present invention, there is provided avideo game processing method for displaying a virtual space viewed froma virtual viewpoint on a screen. The method includes obtaining a simplemodel, which bounds a polygon group of an object in the virtual space.The method further includes calculating first depth information from theviewpoint and display coordinates with respect to a vertex of the simplemodel. The method further includes obtaining present depth informationfrom the viewpoint with respect to an area corresponding to the displaycoordinates. The method further includes comparing the first depthinformation with the present depth information. The method furtherincludes stopping further processing of the object when the first depthinformation indicates a depth that is deeper than a depth indicated bythe present depth information.

According to the first aspect, the processing can be simplified by usinga simple model so that rendering processing can be performed fast. Thus,a more detailed character or more characters can be displayed.

In the first aspect, obtaining the present depth information may includeobtaining one piece of typical depth information for each of multipledisplay coordinates in the area. Also, comparing may include comparingthe first depth information with the typical depth information. Thus,the depth information to be processed can be summarized, and therendering processing can be performed faster.

Preferably, in the first aspect, the typical depth information is amaximum value for each of the display coordinates in the area. Thus,only the meaningful depth information is summarized, and the renderingprocessing can be performed confidently.

In the first aspect, the simple model may be a hexahedron having eightvertexes. The area in accordance with the display coordinates may be arectangle. Data of the vertex of the object may be provided withidentification information. In, this case, obtaining the simple model isperformed in accordance with the identification information. Thus, therendering processing can be performed confidently and fast.

According to a second aspect of the present invention, there is provideda video game processing apparatus for displaying a virtual space viewedfrom a virtual viewpoint on a screen. The apparatus includes a firstobtaining system that obtains a simple model, which bounds a polygongroup of an object in the virtual space. The apparatus further includesa calculator that calculates first depth information from the viewpointand display coordinates with respect to a vertex of the simple model.The apparatus further includes a second obtaining system that obtainspresent depth information from the viewpoint with respect to an areacorresponding to the display coordinates. The apparatus further includesa comparator that compares the first depth information with the presentdepth information. Furthermore, the apparatus includes a stopping systemthat stops further processing of the object when the first depthinformation indicates a depth that is deeper than a depth indicated bythe present depth information.

According to the second aspect, the processing can be simplified byusing a simple model so that rendering processing can be performed fast.Thus, a more detailed character or more characters can be displayed.

In the second aspect, the second obtaining system may obtain one pieceof typical depth information for each of multiple display coordinates inthe area. The comparator may compare the first depth information withthe typical depth information. Thus, the depth information to beprocessed can be summarized, and the rendering processing can beperformed faster.

According to the second aspect, the second obtaining system may beimplemented by an image processing unit having an image reductionfunction. The typical depth information for each of the displaycoordinates in the area may be obtained by the image processing unit. Byusing an existing unit such as the image processing unit, an increase inhardware size and/or an increase in costs can be suppressed, and, at thesame time, the rendering processing can be performed faster.

Preferably, in the second aspect, the typical information is a maximumvalue for each of the display coordinates in the area. Thus, only thedepth information, which is meaningful, is summarized, and the renderingprocessing can be performed confidently.

In the second aspect, the simple model may be a hexahedron having eightvertexes. The area corresponding to the display coordinates may be arectangle. Data of the vertex of the object may be provided withidentification information. The data of the vertex of the object ispreferably provided with identification information, and the firstobtaining system may further include a supply system that supplies thedata of the vertex of the object to the first obtaining system inaccordance with the identification information. Thus, the renderingprocessing can be performed confidently and fast.

According to a third aspect of the present invention, there is provideda computer readable recording medium on which is recorded a video gameprogram for displaying a virtual space viewed from a virtual viewpointon a screen. The program causes a computer to obtain a simple model,which bounds a polygon group of an object in the virtual space. Theprogram further causes the computer to calculate first depth informationfrom the viewpoint and display coordinates with respect to a vertex ofthe simple model. The program further causes the computer to obtainpresent depth information from the viewpoint with respect to an areacorresponding to the display coordinates. The program further causes thecomputer to compare the first depth information with the present depthinformation. The program further causes the computer to stop furtherprocessing of the object when the first depth information indicates adepth that is deeper than a depth indicated by the present depthinformation.

According to the third aspect, the processing can be simplified by usingthe simple model, and rendering processing can be performed fast. Thus,a more detailed character or more characters can be displayed.

In the third aspect, obtaining the present depth information may includeobtaining one piece of typical depth information for each of multipledisplay coordinates in the area. Also, comparing may include comparingthe first depth information with the typical depth information. Thus,the depth information to be processed can be summarized, and therendering processing can be performed faster.

Preferably, in the third aspect, the typical depth information is amaximum value for each of the multiple display coordinates in the area.Thus, only the meaningful depth information is summarized, and therendering processing can be performed confidently.

In the third aspect, the simple model may be a hexahedron having eightvertexes. The area corresponding to the display coordinates may be arectangle. Data of the vertex of the object may be provided withidentification information, so that obtaining the simple model isperformed in accordance with the identification information. Thus, therendering processing can be performed confidently and fast.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a video game machine according to anembodiment of the present invention;

FIG. 2 is a flowchart for explaining operations relating to renderingprocessing according to an embodiment of the present invention;

FIG. 3 is a flowchart for explaining operations relating to renderingprocessing according to an embodiment of the present invention;

FIG. 4 is an explanatory diagram for explaining a simple model accordingto an embodiment of the present invention;

FIG. 5 is an explanatory diagram for explaining detection of a Z-areaand generation processing according to an embodiment of the presentinvention; and

FIGS. 6A and 6B are explanatory diagrams each for explaining operationsrelating to the rendering processing according to an embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below withreference to the attached drawings. FIG. 1 is a block diagram showing anexample of a configuration of a video game machine, according to anembodiment of the present invention.

First of all, a video game machine according to an embodiment of thepresent invention will be described. A game machine 10 includes a gamemachine body 11 and a keypad 50 connected to an input side of the gamemachine body 11. A television set 100 having a cathode ray tube (CRT)and a speaker is connected to an output side of the game machine body11.

The game machine body 11 includes a central processing unit (CPU) 12, aread only memory (ROM) 13, a random access memory (RAM) 14, a hard diskdrive (HDD) 15, and a graphics processing portion 16. The game machinebody 11 also includes a sound processing portion 17, a disk drive 18,and a communications interface portion 19. A memory card reader/writer20 and an input interface portion 21 are also provided. All componentsare connected via a bus 22. The game machine body 11 is connected to thekeypad 50 serving as an operation input portion, through the inputinterface portion 21.

A cross key 51 and a button group 52 are provided on the keypad 50. Thebutton group 52 includes a circle button 52 a, an X-button 52 b, atriangle button 52 c and a square button 52 d. A select button 55 isprovided at a joint part between a base having the cross key 51 and abase having the button group 52. Multiple buttons such as an R1 button56 and an L1 button 53 are provided on the side of the keypad 50.

The keypad 50 includes switches linking with the cross key 51, thecircle button 52 a, the X-button 52 b, the triangle button 52 c, thesquare button 52 d, the select button 55, the R1 button 56 and the L1button 53, respectively. When each of the buttons is pressed, thecorresponding switch is turned on. Then, a detection signal inaccordance with ON/OFF of the switch is generated in the keypad 50.

The detection signal generated in the keypad 50 is supplied to the inputinterface portion 21. The detection signal from the keypad 50 passedthrough the input interface 21 can serves as detection informationindicating which button on the keypad 50 is turned on. Thus, anoperation instruction given from a user to the keypad 50 is furthersupplied to the game machine body 11.

The CPU 12 performs overall control of the entire apparatus by executingan operating system stored in the ROM 13. The CPU 12 executes a videogame program stored in a program area of the RAM 14. In addition, theCPU 12 monitors a manipulation state on the keypad 50 through the inputinterface 21 and executes a video game program stored in the programarea of the RAM 14 as necessary. Furthermore, various kinds of dataderived from the progress of a game are stored in predetermined areas,respectively, of the RAM 14 as necessary.

The RAM 14 includes a program area, an image data area, a sound dataarea and an area for storing other data. Program data, image data, sounddata and other data, which are read from a disk 30 such as a DVD and aCD-ROM through the disk drive 18, are stored in respective areas.

The RAM 14 is also used as a work area. Various kinds of data derivedfrom the progress of a game are stored in an area for storing otherdata. Program data, image data, sound data, and other data read from thedisk 30 can be stored in the hard disk drive 15. The program data, imagedata, sound data and other data stored in the hard disk drive 15 may betransferred to the RAM 14 as necessary. Various kinds of data derivedfrom the progress of a game, which are stored in the RAM 14, may betransferred and stored in the hard disk drive 15.

The graphics processing portion 16 includes a frame buffer as a buffermemory for storing image data and a Z-buffer for storing depthinformation in the VRAM 23. The graphics processing portion 16determines whether the object can be displayed, by executing aprocessing as described later, while referring to the z value thatserves as the depth information at the time when the value is writteninto the z buffer in accordance with control information sent from theCPU 12 upon the execution of program. Then, the graphics processingportion 16 stores the object that can be displayed in the frame bufferby Z-buffering. Then, the graphics processing portion 16 generates videosignals based on image data stored in the frame buffer in accordancewith predetermined timing, and outputs the video signal to a televisionset 100. Thus, an image is displayed on a screen display portion 101 ofthe television set 100.

Specifically, image data including color information to be displayed inrespective display coordinates is stored in the frame buffer. A Z-value,serving as the depth information corresponding to image data stored inthe display coordinates of the frame buffer, is stored in the Z-buffer.Based on these kinds of information, the image data stored in the framebuffer is displayed on the screen displaying portion 101 of thetelevision set 100. The graphics processing portion 16 includes an imageprocessing unit having a sprite function for deforming, enlarging andreducing an image. Thus, an image can be processed variously inaccordance with control information from the CPU 12.

The sound processing portion 17 has a function for generating a soundsignal such as background music (BGM), a conversation between charactersand sound effects. The sound processing portion 17 outputs the soundsignals to a speaker 102 of the television set 100 based on data storedin the RAM 14 in accordance with control information from the CPU 12upon program execution.

The television set 100 has the screen display portion 101 and thespeaker 102 and displays images and outputs sound in accordance with acontent of a video game based on video signals and/or sound signals fromthe game machine body 11.

The disk (such as a DVD and a CD-ROM) 30, which is a recording medium,can be removably loaded in the disk drive 18. The disk drive 18 readsprogram data, image data, sound data and other data of a video gamestored in the disk 30.

The communications interface portion 19 is connected to a network 110.The communications interface portion 19 obtains various kinds of data byexchanging data with a data storage device and/or information processingdevice such as a server located in another place. The program data,image data, sound data and other data of the video game stored in theRAM 14 may be obtained via the network 110 and the communicationsinterface portion 19.

A memory card 31 can be removably loaded in the memory cardreader/writer 20. The memory card reader/writer 20 writes a smalleramount of saved data such as progress data of the video game andenvironment setting data of the video game in the memory card 31.

A video game program for displaying a virtual space from a virtualviewpoint on a screen is recorded in a recording medium according to oneembodiment of the present invention, that is, the disk 30. The disk 30is readable by a computer (the CPU 12 and peripheral devices). Byreading and executing the program, the computer can obtain a simplemodel that bounds a polygon group of an object in a virtual space. Thecomputer can also calculate first depth information from a viewpoint anddisplay coordinates with respect to a vertex of the simple model.Furthermore, the computer can obtain present depth information from aviewpoint with respect to an area corresponding to the displaycoordinates and compare the first depth information with the presentdepth information. Furthermore, the computer can stop the execution ofsubsequent steps for the object when the first depth informationindicates a depth that is deeper than a depth indicated by the presentdepth information.

Accordingly, in addition to functions required for performing softwareprocessing based on data stored in memories of the CPU 12 and otherparts and executing a conventional video game by using hardware in thegame machine body 11, the game machine body 11 includes, as uniquefunctions relating to image processing, a first obtaining unit forobtaining a simple model, which bounds a polygon group of an object in avirtual space. The game machine body 11 further includes a calculatingunit for calculating first depth information from a viewpoint anddisplay coordinates with respect to a vertex of the simple model. Thegame machine body 11 further includes a second obtaining unit forobtaining present depth information from a viewpoint with respect to anarea corresponding to the display coordinates. The game machine body 11includes a comparing unit for comparing the first depth information withthe present depth information. The game machine body 11 further includesa stopping unit for stopping the execution of subsequent steps for theobject when the first depth information indicates a depth that is deeperthan the present depth information.

In this case, the second obtaining unit of the game machine body 11includes a function for obtaining one piece of typical depth informationfor each of the multiple display coordinates in the area correspondingto the display coordinates. The comparing unit includes a function forcomparing the first depth information with the typical depthinformation.

Therefore, image processing can be performed fast, and a video game canbe achieved in which a more detailed character or more characters can bedisplayed. In this case, these unique functions may be implemented byspecific hardware.

Next, operations of this embodiment having the construction as describedabove will be described. FIGS. 2 and 3 are illustrative schematicflowcharts showing processing steps involved in the image processingaccording to the embodiment.

First of all, though not shown in FIG. 2, when a system is powered on, aboot program is read out and each of the components is initialized, andprocessing for starting a game is performed. In other words, programdata, image data, sound data and other data stored in the disk (such asa DVD and a CD-ROM) 30 is read out by the disk drive 18, and are storedin the RAM 14. At the same time, if required, data stored in the harddisk drive 15 or a writable nonvolatile memory such as the memory card31, is read out and is stored in the RAM 14.

Various initial settings having been performed so that the game can bestarted, for example, the keypad 50 is manipulated to move a playercharacter. Then, when a request is received for displaying an objectfrom a predetermined viewpoint at the movement position, the processinggoes to step S1. Here, highest values are stored in the Z-buffer.

At step S1, a background model is obtained. A background model is asummary of three-dimensional coordinate data showing a background of animage. When the background model has been obtained, the processing goesto step S2.

At step S2, a Z-value of each of the vertexes of the background modelfrom the predetermined viewpoint and display coordinates of each of thevertexes of the background model are calculated. When the Z-values ofthe background model and the display coordinates of the background modelhave been calculated, the processing goes to step S3. There, the presentZ-values corresponding to the display coordinates of the vertexes of thebackground model, which are stored in the present Z-buffer, and theZ-values calculated at step S2 are compared. Then, it is determinedwhether the present Z-values stored in the Z-buffer at that time arelarger than the Z-values of the vertexes of the background model.

When it is determined at step S3 that the present Z-values stored in theZ-buffer at that time are larger than the Z-values of the vertexes ofthe background models, the processing goes to step S4. There, theZ-values of the vertexes of the background model are stored in theZ-buffer. In addition, the corresponding image data is written in theframe buffer, and the processing goes to step S5. At step S3, when it isdetermined that the present Z-values stored in the Z-buffer are notlarger than the Z-values of the background model, the processingdirectly goes to step S5.

At step S5, it is determined whether the same processing has beenperformed on areas corresponding to all of the vertexes of thebackground model. The processing at steps S3 to S5 is repeated until theprocessing is performed on all of the areas. When it is determined thatthe processing has been performed on the areas corresponding to all ofthe vertexes of the background model, the processing goes to step S6.

At step S6, whether another background exists is determined. If it isdetermined that another background exists, the processing returns tostep S1. Then, processing at steps S1 to S6 is repeated. At step S6,when it is determined that other backgrounds do not exist, theprocessing goes to step S7.

At step S7, a simple model of an object such as a predeterminedcharacter to be processed is obtained. The simple model is a summary ofthree-dimensional coordinate data indicating vertexes of a hexahedron,which bounds a polygon group of the object.

FIG. 4 is an explanatory diagram showing a specific example of thesimple model. FIG. 4 includes a character 400 as an object. Thesquare-pillar like hexahedron bounding the character 400 is a simplemodel. The simple model includes three-dimensional data for eightvertexes, a, b, c, d, e, f, g and h. Referring back to FIG. 3, when thesimple model has been obtained, the processing goes to step S8.

At step S8, a Z-value of each of the vertexes of the simple model from apredetermined viewpoint and the display coordinates of each of thevertexes of the simple model are calculated. When the Z-values of thesimple model and the display coordinates of the simple model have beencalculated, the processing goes to step S9. Then, a rectangular Z-area(described below) is detected based upon the display coordinatescalculated in step S8.

When the Z-area has been detected, an area reduced to apredetermined-size is generated based upon the detected Z-area whileleaving the features of the detected Z-area. Here, the sprite functionof the image processing unit provided in the graphics processing portion16 is used. Since the unit for executing specific processing is used inthis way, the processing can be performed fast. The scale of hardwaredoes not have to be increased because the existing unit is used. Also,additional costs are not required.

FIG. 5 is an explanatory diagram conceptually showing an example of thedetection of the Z-area corresponding to the display coordinates and thegeneration of the area of the predetermined size based upon the Z-area.In FIG. 5, an area 401 is a z-buffer having an area corresponding to adisplay screen having 600×400 pixels.

Here, for example, when the Z-area corresponding to eight vertexes ofthe simple model shown in FIG. 4 is detected through the processing atstep S9, a rectangular area 402 in FIG. 5 is detected as the Z-areacorresponding to the display coordinates.

In the example shown in FIG. 5, a (64×64) rectangular area is detectedas the Z-area. However, the size of the rectangular area may be detecteddifferently according to viewpoints and/or directions of the object. Forexample, when a viewpoint exists at a position directly across from thecenter of the front surface of the character 400, a rectangular areahaving four vertexes (a, b, c and d) at the corners is detected as theZ-area, which is different in size.

Then, an area of a predetermined size of, for example, 32×32 pixels isgenerated based upon the area 402 of 64×64 pixels as shown in FIG. 5, byusing the sprite function of the image processing unit of the graphicsprocessing portion 16 while leaving the characteristics of the detectedZ-area. For example, the highest one of the Z-values in every Z-areacorresponding to four adjacent pixels is extracted as a typical value.The typical values of the entire area 402 are extracted so that the areaof the predetermined size of 32×32 is generated based upon the area 402.

The generation of the reduced size (32×32) area in this way can keep anamount of comparison processing in subsequent steps within a certainrange. In this example, because the highest value is used as the typicalvalue, the data compression does not affect the subsequent steps.Alternatively, an average value of the Z-values within the areacorresponding to multiple pixels may be used as the typical value, whichalso contributes to faster processing.

When the generation of the area of the predetermined size has completed,the processing goes to step S11. At step S11, a minimum value Z1MIN ofthe simple model is extracted. Then, the minimum value Z1MIN of thesimple model and all of the Z-values within the generated area, whichare stored in the Z-buffer at the present time, are compared. Then, amaximum z-value Z2MAX within the generated area is extracted, and it isdetermined whether the minimum value Z1MIN of the simple model is largerthan the maximum value Z2MAX.

At step S11, when it is determined that the minimum value Z1MIN of thesimple model is larger than the maximum value Z2MAX within the generatedarea, the object cannot be seen from the viewpoint because of thebackground, for example, displayed at the present time. Thus, steps S12to S16 are skipped. Then, the processing goes to step S17. In this way,processing by using a real model of the object, which does not have tobe displayed, is not executed. As a result, the processing can beperformed faster. When it is determined that the minimum value Z1MIN ofthe simple model is not larger than the maximum value Z2MAX within thegenerated area, the processing goes to step S12.

At step S12, real model data is obtained for the object of thepredetermined character to be processed. The real model data is asummary of three-dimensional coordinate data indicating vertexes of theobject (for example, character 400 in FIG. 4). When the real model hasbeen obtained, the processing goes to step S13.

At step S13, Z-values of vertexes of the real model from a predeterminedviewpoint and display coordinates of vertexes of the real model arecalculated. When the Z-values of the vertexes of the real model and thedisplay coordinates of the real model have been calculated, theprocessing goes to step S14. Then, the Z-values stored in the Z-bufferat the present time at a position corresponding to the displaycoordinates of the vertexes of the real model are compared with theZ-values of the vertexes calculated at step S13. Then, it is determinedwhether the Z-values stored in the Z-buffer at the present time arelarger than the Z-values of the vertexes of the real model.

At step S14, when it is determined that the Z-values stored in theZ-buffer at the present time are larger than Z-values of the vertexes ofthe real model, the processing goes to step S15. At step 15, theZ-values of the vertexes of the real model are stored in the Z-buffer,and image data is written in the frame buffer. Then, the processing goesto step S16. Alternatively, at step S14, when it is determined that theZ-values stored in the Z-buffer at the present time are not larger thanthe Z-values of the vertexes of the real model, the processing goes tostep S16 directly.

At step S16, it is determined whether the same processing is performedon the areas corresponding to all of the vertexes of the real model.Steps S14 to S16 are repeated until the processing is performed all ofthe areas. When it is determined that the processing is performed on theareas corresponding to all of the vertexes of the real model, theprocessing goes to step S17.

At step S17, it is determined whether any other target objects exists.If it is determined that another object exists, the processing returnsto step S7. Then, steps S7 to S17 are repeated. If it is determined thatno other objects exist at step S17, the processing goes to step S18.

At step S18, display processing is performed on the objects of thepredetermined characters to be processed, and images for thepredetermined objects are displayed on a screen. Then, the processingends, and highest values are stored in the Z-buffer.

FIGS. 6A and 6B are explanatory diagrams showing positionalrelationships of three objects to be processed. Operations relating tothe rendering processing according to this embodiment will be describedmore specifically with reference to FIGS. 6A and 6B.

In FIGS. 6A and 6B, a reference numeral 501 represents a viewpoint. FIG.6A shows a positional relationship of objects within a viewing angle onan XZ-plane. FIG. 6B shows a positional relationship of objects within aviewing angle on a ZY-plane. Each of FIGS. 6A and 6B includes abackground model 502 and simple models 503 and 504 for the objects to beprocessed. Here, the Z-values serving as depth information are stored inthe Z-buffer.

First, the simple model 503 to be processed exists in front of thebackground model 502 with respect to the viewpoint 501. Therefore, it isdetermined that the minimum value Z1MIN of the simple model is notlarger than the maximum value Z2MAX within the generated area of thepredetermined size. As a result, a real model thereof is obtained andundergoes general processing. Thus, the Z-values of vertexes forming theobject bounded by the simple model 503 are written in the Z-buffer. Inaddition, image data is written in the frame buffer.

The simple model 504 to be processed is positioned behind the backgroundmodel 502 with respect to the viewpoint 501. Therefore, it is determinedthat the minimum value Z1MIN of the simple model is larger than themaximum value Z2MAX within the generated area. Thus, the subsequentsteps are skipped. The real model is not obtained and does not undergogeneral processing for the vertexes. In addition, no writing isperformed on the Z-buffer and the frame buffer.

Next, another embodiment will be described. According to theabove-described embodiment, the rectangular Z-area corresponding to thedisplay coordinates calculated from the simple model is detected at stepS9, and after the completion of the Z-area detection, the processinggoes to step S10 directly. In another embodiment, it may be determinedthat the Z-area is equal to or smaller than the predetermined area. Whenit is determined that it is equal to or smaller than the predeterminedarea, the Z-area may be replaced with the generated area directly. Then,the processing may go to step S11. When it is determined that the Z-areais larger than the predetermined area, the processing goes to step S10,where the area of the predetermined size is generated with the featuresof the Z-area. Such processing can suppress the amount of processinginvolved in comparisons at subsequent steps. Thus, more efficientprocessing can be achieved.

According to the above-described embodiment, a square-pillar (havingrectangular planes) like hexahedron having eight vertexes, whichaccommodates an object, is used. However, other solids may be used as asimple model. For example, a triangle-pillar (having rectangular planes)like pentahedron having six vertexes, which accommodates an object maybe used as the simple model. A simple hexahedron may be used instead ofthe one in the shape of the rectangular-pillar (having rectangularplanes).

Furthermore, in the above-described embodiment, the simple model isobtained before the processing on the real model with respect to theobject for a character. Alternatively, in another embodiment, objectsmay be divided into two groups in accordance with identification dataattached to data of vertexes of object. With respect to the objectsbelonging to one group, the determination processing is performed basedon the simple model. With respect to the objects belonging to the othergroup, the real model itself is processed.

Although the invention has been described with reference to severalexemplary embodiments, it is understood that the words that have beenused are words of description and illustration, rather than words oflimitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the invention in its aspects. Although the inventionhas been described with reference to particular means, materials andembodiments, the invention is not intended to be limited to theparticulars disclosed; rather the invention extends to all functionallyequivalent structures, methods, and uses such as are within the scope ofthe appended claims. In addition, the components having the samefunctions are assigned the same reference numerals, in respectivefigures.

As described above, according to these embodiments, a simple model isused such that rendering processing can be performed fast. Thus, a moredetailed character or more characters can be displayed, for example.

1. A video game processing method for displaying a virtual space viewedfrom a virtual viewpoint on a screen, comprising: obtaining a threedimensional simple model that bounds a polygon group of a threedimensional object in the virtual space; calculating first depthinformation from the viewpoint and display coordinates with respect to avertex of the simple model; obtaining present depth information from theviewpoint with respect to an area corresponding to the displaycoordinates, the area comprising a rectangle bounding all vertexes ofthe simple model as viewed from the viewpoint, the area varying when theviewpoint changes and/or when an orientation of the object changes;comparing the first depth information and the present depth information;and stopping further processing of the object when the first depthinformation indicates a depth that is deeper than a depth indicated bythe present depth information.
 2. The video game processing methodaccording to claim 1, wherein obtaining the present depth informationfurther comprises obtaining one piece of typical depth information foreach of a plurality of display coordinates in the area, and comparingfurther comprises comparing the first depth information with the typicaldepth information.
 3. The video game processing method according toclaim 2, wherein the typical depth information comprises a maximum valuefor each of the display coordinates in the area.
 4. The video gameprocessing method according to claim 1, wherein the simple modelcomprises a hexahedron having eight vertexes.
 5. The video gameprocessing method according to claim 1, wherein identificationinformation is added to data of the object, and wherein, when theidentification information indicates that the simple model is used, thecalculating the first depth information and display coordinates isperformed.
 6. The video game processing method according to claim 1,wherein obtaining the present depth information further comprisestransforming the area corresponding to the display coordinates; and thepresent depth information with respect to an area corresponding to thedisplay coordinates is the depth information with respect to thetransformed area corresponding to the display coordinates.
 7. A videogame processing apparatus for displaying a virtual space viewed from avirtual viewpoint on a screen, comprising: a first obtaining system thatobtains a three dimensional simple model bounding a polygon group of athree dimensional object in the virtual space; a calculator thatcalculates first depth information from the viewpoint and displaycoordinates with respect to a vertex of the simple model; a secondobtaining system that obtains present depth information from theviewpoint with respect to an area corresponding to the displaycoordinates, the area comprising a rectangle bounding all vertexes ofthe simple model as viewed from the viewpoint, the area varying when theviewpoint changes and/or when an orientation of the object changes; acomparator that compares the first depth information with the presentdepth information; and a stopping system that stops further processingof the object when the first depth information indicates a depth that isdeeper than a depth indicated by the present depth information.
 8. Thevideo game processing apparatus according to claim 7, wherein the secondobtaining system obtains one piece of typical depth information for eachof a plurality of display coordinates in the area; and the comparatorcompares the first depth information with the typical depth information.9. The video game processing apparatus according to claim 8, wherein thesecond obtaining system is implemented by an image processing unithaving an image reduction function, and the typical depth informationfor each of the display coordinates in the area is obtained by the imageprocessing unit.
 10. The video game processing apparatus according toclaim 8, wherein the typical depth information comprises a maximum valuefor each of the display coordinates in the area.
 11. The video gameprocessing apparatus according to claim 7, wherein the simple modelcomprises a hexahedron having eight vertexes.
 12. The video gameprocessing apparatus according to claim 7, wherein identificationinformation is added to data of the object, and the first obtainingsystem further comprises a supply system, wherein, when theidentification information indicates that the simple model is used, thesupply system supplies the data of the object to the first obtainingsystem.
 13. The video game processing apparatus according to claim 7,wherein the second obtaining system that obtains the present depthinformation further comprises a transforming system that transforms thearea corresponding to the display coordinates; and the present depthinformation with respect to an area corresponding to the displaycoordinates is the depth information with respect to the transformedarea corresponding to the display coordinates.
 14. A computer readablerecording medium on which is recorded a video game program fordisplaying a virtual space viewed from a virtual viewpoint on a screen,the program causing a computer to execute: obtaining a three dimensionalsimple model bounding a polygon group of a three dimensional object inthe virtual space; calculating first depth information from theviewpoint and display coordinates with respect to a vertex of the simplemodel; obtaining present depth information from the viewpoint withrespect to an area corresponding to the display coordinates, the areacomprising a rectangle bounding all vertexes of the simple model asviewed from the viewpoint, the area varying when the viewpoint changesand/or when an orientation of the object changes; comparing the firstdepth information with the present depth information; and stoppingfurther processing of the object when the depth information obtained bythe first depth information indicates a depth that is deeper than adepth indicated by the present depth information.
 15. The computerreadable recording medium according to claim 14, wherein obtaining thepresent depth information further comprises obtaining one piece oftypical depth information for each of the plurality of displaycoordinates in the area; and comparing further comprises comparing thefirst depth information obtained with the typical depth information. 16.The computer readable recording medium according to claim 15, whereinthe typical depth information comprises a maximum value for each of thedisplay coordinates in the area.
 17. The computer readable recordingmedium according to claim 14, wherein the simple model comprises ahexahedron having eight vertexes.
 18. The computer readable recordingmedium according to claim 14, wherein identification information isadded to data of the object, and wherein, when the identificationinformation indicates that the simple model is used, the calculating thefirst depth information and display coordinates is performed.
 19. Thecomputer readable recording medium according to claim 14, whereinobtaining the present depth information further comprises transformingthe area corresponding to the display coordinates; and the present depthinformation with respect to an area corresponding to the displaycoordinates is the depth information with respect to the transformedarea corresponding to the display coordinates.